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hash_map will this work?

General and Gameplay Programming Programming

Started by lucky6969b January 28, 2012 02:23 PM

7 comments, last by SiCrane 12 years, 2 months ago

lucky6969b

1,334

Author

January 28, 2012 02:23 PM



stdext::hash_map<Coord *, bool> m_SparseMap;



void CooperativeTable::ReservePos(Coord* pos)

{

   m_SparseMap[pos] = false;

}

Will the compiler automatically sort out the correct index and buckets i need?
Coord contains x,y and time i think
Thanks
Jack

Antheus

2,410

January 28, 2012 04:21 PM

Will the compiler automatically sort out the correct index and buckets i need?[/quote]

What would "correct" mean in this case? What do you "need"?

lucky6969b

1,334

Author

January 28, 2012 04:36 PM

I want to hash a key of combination of a coordinate plus its time...
By the time of response, i have separate time and location into 2 tiers.
Thanks for helping
Jack

SiCrane

11,840

January 28, 2012 04:54 PM

Probably not. It most likely will use a hash based on the value of the pointer by default, not what the pointer points to.

lucky6969b

1,334

Author

January 28, 2012 05:27 PM

How about converting Coord* into pointers
int *x;
int *y;
int *time;
Thanks
Jack

SiCrane

11,840

January 28, 2012 05:37 PM

[color=#282828][font=helvetica, arial, verdana, tahoma, sans-serif]

If it creates a hash based on the pointer value, and not what it points to, it doesn't matter if it points to values or if it points to pointers. It won't care either way.
[/font]

lucky6969b

1,334

Author

January 29, 2012 09:54 PM

How would I design a hash_map that has x,y,time as keys and score as output?
Could you please give an example?
Thanks
Jack

_the_phantom_

11,263

January 29, 2012 10:57 PM

You would need to supply a hashing function which could deal with the object type and generate a hash accordingly.

For example our hash_map at work allows keys of char * by having a hashing function which knows that a char * is a 'string' and that it should has what it points to rather than the value the pointer holds.

SiCrane

11,840

January 29, 2012 11:04 PM

Assuming you're referring to the MSVC stdext::hash_map class, the best course would probably to use a struct/class key type instead of a pointer. Then provide a hash_value() function that takes that struct type and returns a hash and overload operator< for your type.

hash_map will this work?

If it creates a hash based on the pointer value, and not what it points to, it doesn't matter if it points to values or if it points to pointers. It won't care either way.
[/font]

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hash_map will this work?

If it creates a hash based on the pointer value, and not what it points to, it doesn't matter if it points to values or if it points to pointers. It won't care either way.[/font]

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If it creates a hash based on the pointer value, and not what it points to, it doesn't matter if it points to values or if it points to pointers. It won't care either way.
[/font]